Need the spark plug gap for 90 geo tracker...

Without the manual, the spark gap is usually 18-22thou.

correct spark plugs.
gapped to under hood sticker gap>? (EPA sticker)
replace wires 1 by 1 not mixing wires up>? oops?
knocked off a critical sensor? map or maf.
is the check engine light on , running,
yes, then scan it. scan the OBD2 port at ,knees.
its telling you what you did wrong. listen to it.

open hood ,
look up, see that EPA sticker there?, it shows 0.028"
its a range really but low size is best.
http://www.fixkick.com/IGN_timing/tune-ups.html#SPARK16

Do them one at a time if not you need to know the firing order

Check fuse, check bulbs.

correct plugs or gap...firing order correct? unplugged coil or distributor lead

0.42

.045

Assuming this is a DOCH 2.0 engine, .044 (In thousandths of an inch)
(from autozone.com)

If plug wires are arcing at any point, replace plug wires and recheck.